An obscure turn of phrase.An impulse to go off and fight certain obscure battles of his own spirit.Their descriptions of human behavior become vague, dull, and unclear.Vague...forms of speech...have so long passed for mysteries of science.

source: WordNet 3.0

lacking clarity or distinctness

A dim figure in the distance.Only a faint recollection.Shadowy figures in the gloom.Saw a vague outline of a building through the fog.A few wispy memories of childhood.